Sometimes, Tonks wonders if she and Luna have anything in common. From dawn to dusk their lives are different: Tonks eats porridge for breakfast the way her parents always did, warm and filling, whereas Luna eats whatever she feels like: sushi, chocolate ice cream, freshwater plimpy soup with croutons.

"There have to be croutons," Luna explained, when Tonks enquired. "Otherwise it wouldn't be breakfast."

Tonks is at work by 8 every morning, except for the days she's on night shift, while Luna starts work whenever she feels like it. Frequently she sleeps until noon, blonde hair spread across the brightly coloured pillows, and then stays up until 3 or 4 in the morning writing up her field notes and drawing exotic animals by candlelight.

"How can you see to work?" Tonks asked, yawning, the first time she woke in the night and found Luna missing from the bed.

"Oh, there's more light now than when I saw it in Belize," Luna said airily, as she picked up another coloured pencil and added dark green stripes to the rump of the creature. In the flickering candlelight, it looked real enough to get up and walk off the page.

"You do research at night?" said Tonks stupidly — not her finest moment, but nobody's deductive skills are at their best right after waking up.

"I follow the animals," Luna replied, looking up. Her eyes met Tonks' as she said, "Just like you follow the criminals. A lot of animals prefer darkness."

A lack of lunch-breaks is one of the occupational hazards of being an Auror, so Tonks usually comes home from work famished. Left to her own devices she cooks simple, filling food: pasta, Shepherd's pie, meat and two veg. Occasionally she branches out by attempting a curry or a stir-fry, although she's more likely to buy those from a takeaway on the journey home.

Luna's cooking is famously experimental, and the results are never the same twice. The best home-cooked meal Tonks has ever eaten was made by Luna, but so were the nine worst meals of her life.

"I don't think that's meant to be a dessert," Tonks said, the time she came home to find Luna making custard with tomatillos.

"Meant by who?" said Luna, blowing her hair out of her eyes. "I mean it to be a dessert."

"Meant by the people who grew them," Tonks replied, stepping forward. She caught the errant lock of Luna's hair and tucked it behind her ear, fingers carefully avoiding the earring that dangled there.

"Why should they determine its destiny?" Luna asked, stirring the pan, where tomatillos bobbed amidst a bright yellow sauce. "Our parents grew us, but they don't get to choose what we make of ourselves."

"Fair enough," Tonks said, sliding an arm around Luna's waist.

"Would your mum and dad have chosen this for you?"

"Tomatillos in custard? Not a chance," Tonks joked.

Luna just kept stirring and waited for the answer.

"Maybe not at first," said Tonks, thinking of the naked fear on her mother's face when she had announced her intention to join the Aurors, and her parents' carefully polite expressions when she introduced them to Luna.

There were probably still moments when her parents wished things had turned out differently, like a couple of hours into Christmas dinner with Xenophilius. If Tonks is absolutely honest, she has occasional spasms of doubt herself, and experienced several as she steered Luna through the crowds at the Auror's Ball last year.

She might never forget Kingsley's expression as Luna explained to him how as Minister of Magic, he was the only one capable of stopping the Rotfang Conspiracy. I'll nod and smile because you're my friend his face said, but if we hadn't been in the Order together, Tonks, your prospects for promotion would be toast.

Yes, there were rocky moments, but on average it worked. If Xenophilius, her parents, or even Kingsley saw the two of them now, Tonks was pretty sure they would smile.

"They've got used to it. Now, I don't think they'd want anything else for me."

"That's my hope for the tomatillos," Luna replied, still stirring. "It's such a pretty word, so I thought it needed eggs and sugar. Tom-ah-tillo."

"We'll see how it turns out," said Tonks, kissing her cheek.

The custard, predictably, was horrible. Six months later, after the exploding tamarind lasagne incident, they agreed that Luna would only make experimental dinners on days when Tonks wasn't working and felt up to a challenge.

Tonks likes her life to happen on a schedule: beer at the Leaky on Friday, groceries on Saturday, laundry on Sunday, and tea with her mum and dad once a week. Luna, by contrast, doesn't seem to do anything regularly: she buys groceries when she's hungry and does laundry when she runs out of clothes.

"I don't know how you live like this!" Tonks told her once, in exasperation.

"I don't know who I'll be tomorrow, so how would I know what I'll want?" Luna explained, with characteristic Lovegood logic.

"But you'll want to wear clothes whatever mood you're in," Tonks pointed out.

"Not necessarily," Luna said, eyes sparkling. "Remember when we spent three days together without wearing clothes?"

Luna is utterly, maddeningly, infuriatingly herself. She couldn't be mistaken for anybody else, and sometimes Tonks wishes that she'd be a little more conventional, or at least more willing to compromise. At other times, like two weeks into Luna's three-month research trip to South America, she finds herself craving the spontaneity and experimental cooking.

They're so different that she doesn't understand why it works, but somehow it does work.

"You were born under different stars," her mum said, the night Tonks Apparated to their house and announced that she couldn't go home until Luna removed the stinking corpse of a gigantic horned creature that was filling their living room.

"I'll make a pot of tea," said her dad.

After three cups of tea, half a tin of ginger newts, and a generous helping of stew — Tonks really was starving after work — she was calm enough to Floo home.

"Did you and dad have these sort of problems?" she said, on the doorstep.

Her parents glanced at each other.

"No," her father said loyally.

"Yes," said her mum. "It took me a while to adjust to living with a Muggleborn and not having house elves. And your dad had to get used to living with someone so..."

"Bossy," said Tonks.

"Forthright," her dad said.

"Imperious," her mum finished, with a smile. "You'll both get used to it."

"And if you don't, we've another tin of ginger newts in the cupboard," said her dad.

Little by little, Tonks supposes that she's got used to it. It wasn't a surprise when Luna worked late last night, nor when she came downstairs this morning to a stack of newly written parchment on the dining table — the first draft of the book Luna has a contract for. It's not a surprise now, when Luna comes downstairs wearing nothing but bright purple knickers.

"Morning," Tonks says, lowering the Daily Prophet. "What are your plans for the day?"

"Not wearing clothes," Luna says with a smile, walking towards her. She's the only person Tonks knows whose smile lights up the room.

"You've got pants on."

"I'm hoping you'll want to take them off," Luna says, straddling Tonks' knees and settling herself onto her lap.

Three things go through Tonks' mind in quick succession: 1) doesn't she want breakfast first? 2) in the living room? and 3) fuck it.

Tonks curls her left hand around Luna's neck and kisses her. Luna's lips are warm and soft, parting as her tongue licks into Tonks' mouth. She's always loved the way Luna kisses — as an erotic act in itself, the main course in their meal, instead of a starter. It's probably not a coincidence that Luna is fantastic at oral sex.

"Happy to oblige," Tonks murmurs, and feels Luna smile against her mouth.

Tonks drops the newspaper onto the floor, and grabs Luna's bum. It's a good bum, and she enjoys the sight of it on a regular basis, but nothing beats squeezing it. Luna arches her back, pressing into Tonks' hand, and deepens the kiss.

She squeezes Luna's bum again, just because she can, and then lets her hand drift downwards, tracing the edge of Luna's pants. Luna's breath hitches as Tonks' fingers brush the skin between her thighs.

It's probably possible to fuck Luna in this position, but the angle would give her a sore wrist, and if they're going to be naked all day then Tonks has to conserve her energy. She moves her arm, feeling Luna wriggle in disappointment at the loss, and then places her hand on Luna's belly instead.

"Up," Tonks orders, and Luna shifts her weight just enough that Tonks can slide her hand between their bodies.

Immediately she feels how wet Luna is, the fabric of her pants soaked through. Fucking in this position, Tonks' trousers are going to get smeared, damp and sex-scented, but since she has a schedule and tomorrow is laundry day, that's not a problem.

Luna gasps as Tonks presses her fingers against the wet cotton, right over Luna's clit.

"Not sure I need to take them off," she says, letting her fingers establish a rhythm, and feels Luna's body start to sway in time.

Luna is beautiful like this: head thrown back, blonde hair trailing down her back and her breasts jutting out. Luna might be comfortable in the darkness, but Tonks has always preferred to have sex in the light — why would she pass up a view like this?

"Mmmn," Luna says, a sound that's almost a purr, and grinds her body down against Tonks' fingers. Her pale eyelashes flutter shut.

Tonks smiles, and raises her free hand to cup Luna's breast.

The lack of inhibition with which Luna has sex is one of the qualities she loves most — Luna is fully at ease in the world of sensation and emotion in a way that so few women are. Perhaps it's easier to have great sex if you don't believe in "unitary reason" (as Luna puts it), let alone conventional morality. Not that Tonks is a big fan of conventional morals either, come to that.

She might be notoriously clumsy, but if Tonks concentrates then she has enough coordination to rock the fingers of her right hand over Luna's clit and brush her left thumb back and forth over Luna's nipple. Judging by Luna's little gasps and urgent hip movements, she won't have to keep up the coordination for long.

Tonks runs her nail across the nipple and grins when it elicits a moan. Focusing, she presses her hand harder against Luna's crotch, bicep straining, and Luna pushes back. Luna's inner thighs start to tremble, and it's like watching the beginning of an earthquake: Luna's legs, belly, then shoulders begin shaking, her face screws up, body shuddering more and more violently until the tension bursts as she comes in pulses against Tonks' hand.

"Mmmn," Luna says again, her full weight sinking onto Tonks' lap. She leans forward, resting her temple against Tonks' head, and Tonks wraps an arm around Luna to steady them.

Luna's exhalations puff over her cheek, so Tonks can feel her breathing steady out.

"I think I'll count that as breakfast," says Luna, with a smile in her voice.

"Breakfast?" Tonks says, glancing at the clock above the fireplace. "It's two-o-clock. You're overdue for lunch."

Luna shifts in her lap and presses a kiss to the sensitive skin behind Tonks' ear, sending little shivers down her spine.

"Then we'd better have lunch straight away," Luna says seriously.

Tonks leans back on the sofa, spreading her arms wide, and Luna smiles down at her.

"My plan was for neither of us to wear clothes," Luna tells her.

"I didn't get the memo early enough. You'll just have to take my clothes off."

Luna reaches for the top button of Tonks' shirt, unfastens it, and then bends her head to kiss the triangle of newly revealed skin. Tonks watches her fingers catch the next button, undo it, and then Luna drops a kiss on Tonks' breastbone.

"Could be a slow process."

"Sometimes being naked is a journey, not a destination," says Luna.

Right now, Tonks isn't disposed to argue. The weekend stretches out ahead of them, and there will be time enough for groceries, laundry, experimental cooking, and not wearing any clothes.

Whatever stars we were born under must be smiling, Tonks thinks. Then she banishes any remaining thoughts and closes her eyes, focusing on the delicious sensations of Luna's lips and tongue against her skin.